Page 264 - Synthetic Fuels Handbook

250 CHAPTER EIGHT

implies additional costs compared to the air-blown gasification, because of the oxygen
production. Nevertheless, the energy and financial cost of producing oxygen seems to
be far lower than the alternative energy and financial cost of removing nitrogen from the
product gas from air-blown gasification. This is partly due to the fact that the production
of high-purity oxygen (above 95 percent O ) is a mature technology.
2
In principle, the larger the carbon and hydrogen content in raw materials, employed
in gas-to-liquids processing, is, the easier and more efficient the carbon monoxide and
hydrogen. Hence, the natural gas pathway is the most convenient one, since natural gas is
gaseous and contains virtually carbon and hydrogen only. Solid raw materials (biomass,
coal) involve more processing, because first they have to be gasified and then the obtained
product gas should be cleaned up from other components such as nitrogen oxides (NO ),
x
sulfur oxides (SO ), and particulate matter to the extent of getting as high as possible purity
x
of syngas. Two basic types of biomass raw material are distinguished, namely, woody mate-
rial and herbaceous material. Currently woody material accounts for about 50 percent of
total world bioenergy potential. Another 20 percent is straw-like feedstock, obtained as a
by-product from agriculture. The dedicated cultivation of straw-like energy crops could
increase the herbaceous share up to 40 percent (Boerrigter and van der Drift, 2004; van der
Drift et al., 2004).

8.5 USES

Biomass currently supplies 14 percent of the world’s energy needs, but has the theoretical
potential to supply 100 percent. Most present day production and use of biomass for energy
is carried out in a very unsustainable manner with a great many negative environment con-
sequences. If biomass is to supply a greater proportion of the world’s energy needs in the
future, the challenge will be to produce biomass and to convert and use it without harming
the natural environment. Technologies and processes exist today which, if used properly,
make biomass-based fuels less harmful to the environment than fossil fuels. Applying these
technologies and processes on a site specific basis in order to minimize negative environ-
ment impacts is a prerequisite for sustainable use of biomass energy in the future.
Biodiesel and bioethanol are widely used in automobiles and freight vehicles. For exam-
ple, in Germany most diesel fuel on sale at gas stations contains a few percent biodiesel, and
many gas stations also sell 100 percent biodiesel. Some supermarket chains in the United
Kingdom have switched to running their freight fleets on 50 percent biodiesel, and often
include biofuels in the vehicle fuels they sell to consumers, and an increasing number of
service stations are selling biodiesel blends (typically with 5 percent biodiesel).
In Europe, research is being undertaken into the use of biodiesel as domestic heating
oil. A blend of 20 percent biodiesel with 80 percent kerosene (B20) has been tested suc-
cessfully to power modern high-efficiency condensing oil boilers. Boilers needed a preheat
burner to prevent nozzle blockages and maintain clean combustion. Blends with a higher
proportion of biodiesel were found to be less satisfactory, owing to the greater viscosity of
biodiesel than conventional fuels when stored in fuel tanks outside the building at typical
U.K. winter temperatures.
Different combustion engines are being produced for very low prices lately. They allow
the private house-owner to utilize low amounts of weak compression of methane to gener-
ate electrical and thermal power (almost) sufficient for a well insulated residential home.
Direct biofuels are biofuels that can be used in existing unmodified petroleum engines.
Because engine technology changes all the time, exactly what a direct biofuel is can be hard
to define; a fuel that works without problem in one unmodified engine may not work in